With the continuous development of high-power self-turn devices and intelligent high-speed micro-control chips, high-power power electronic converter devices have become increasingly in-depth research, and the application range of large-capacity motor drives, DC power transmission. More and more extensive. In the implementation of high-power power electron beam devices, an important issue is that high power devices have low operating frequencies and unable to adapt to excellent modulation techniques such as PWM technology. Carrier Phase-Shifted SPWM, CPS-SPWM below is to solve the problem.
Tennessee University PenG F.z. et al. Proposed topology of cascaded H bridge converters in 1996 and used for reactive power compensation [1]. The main circuit topology of the cascaded H bridge converter is shown in FIG. The n single-phase full bridge module is connected in series in the alternating flow side, and the DC side is independent of each other, as shown in FIG. 1 (a). A three-phase system is configured by a three bridge arms, as shown in FIG. 1 (b), as shown in FIG. 1 (b). This cascaded H bridge converter has the following advantages with respect to the diode clamp type multi-level converter and a flying-saving multi-level converter.
1) Each converter unit structure is the same, easy to implement modular design, installation, maintenance;
2) Direct side is independent of each other, and the voltage equalization is easy to implement;
3) Each converter unit works symmetrical, switch load balance.
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In the voltage type conversion circuit. The output AC voltage is a rectangular wave. Early techniques used to multiplex several combined into a rectangular wave output of the sine wave approximation. To increase the capacity, reduce the harmonics for the LX three-phase variable stream circuit unit (each unit three phase, here, using LX, using LX), the number of cells of the three-phase converter in the multipart, and the unit of the H bridge is indicated by the following N Number distinction, this paper is distinguished by each 3-H bridge as a unit), the phase of the output waveform is exempted to π / (3LX), together with a transformer (shifting transformer) that counteracts the phase difference between them, can constitute a pulse number of 6LX The converter system. The output waveform contains a harmonic of 6klx ± 1 (k as positive integers). However, the presence of multiple techniques: the structure is complex, the system dynamic response is poor; the input / output waveform of each device must be displaced to a certain phase, resulting in fundamental loss.
Multi-level combined converters are converters that combine CPS-SPWM technologies and multiple techniques. The type of converter is equivalent to high, small switching, fast dynamic response, communication bandwidth, easy to adopt different control policies. H Bridge Topology In the basic topology of multi-level translucers, there is a simple structure, a minimum number of devices, does not require a large number of clamp diodes and flying over capacitors, easy to modularize and adopt softswitch technology. This paper introduces several basic structures and its cascaded shapes in this paper, and takes a cascaded 3-h bridge as an example. The TMS3201LF2407 DSP issues a pulse signal for the three-phase single module and the single-phase two module H bridge, which outputs three-phase three levels and single-phase five levels, respectively. Spectrum analysis suggests that only the switch is completed and its ribbon harmonic, and the theoretical analysis is completely consistent.
1 H bridge topology
There are two basic structures of the H-bridge multi-level transformer: a three-level H bridge (3-Level H-HRIDGE.3-H), another is a five-level H bridge (5-level H -bridge, 5-h). Among them, the five level H bridges include two types of diode clamp type and capacitance clamp type. The basic unit of the 3-h bridge converter is shown in FIG. 1, which can generate 3 level output: while conducting S1 and S3 or S2 and S4, it can generate polarity between the two bridge arms. Flat; when S1 and S2 or S3 and S4 are simultaneously turned on. Then the zero level is output.
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The basic unit of the 5-H bridge converter is shown in Figure 2. With a pole clamp type as an example, the level generation is explained, and the 5-H unit shown in Fig. 2 (a) is composed of a full bridge midpoint clamping circuit, appropriately changing the switch state of the transistor in the inverter. , A points and N points can be connected to D0, D1, and D2. It is assumed that the DC side voltage Vdc is 2e, the voltage on the capacitor is the VDC / 2.5-H bridge basic unit output voltage VAN may have five different values: -2e, -e, 0, e, and 2e. In this topology, the voltage on the capacitor can be balanced by the selection of redundant states.
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Based on the basic circuit units in FIGS. 1 and 2, the cascaded 3-H converter and the sections shown in Fig. 4 may be obtained. The voltage type inverter coated by 3 H-Class has been invented by Robin Kang Company and applying for a patent, named a perfect-wound inverter. Depending on the system to the output voltage and the number of levels, the number of units can be determined. Cascaded 3-h bridge-type converter has many advantages: When the same level output is output, the components used are minimized; each converter unit is the same, easy to modularize juice and packages; The unit is relatively independent, easy to introduce soft switch control; the average pressure of the DC side is easier to implement; the workload of each converter unit is consistent. For cascaded 3-H converters, cascading unit N (each 3-H converter is a unit) and the number of output waveform levels satisfy W = 2N + L; cascaded 5- The corresponding relationship between the H converter is: w = 4n + L. The independent direct source voltage value of each converter unit is the same. If the voltage values of each independent voltage source are taken as E, 2E, 4E ... 2N-1E, the number of levels thereof is greatly increased to 2N + 1 1 L, that is, the so-called improved level is obtained. The H-bridge type multi-level converter (Modified Cascade No H-Bridgemultilevel Converter). However, the number of such topologically transportation is increased, and the switching loss is increased. The overall efficiency of the circuit is lowered, and the modulation strategy is complicated, and it is still in the exploration phase. , Reading the full text, the technology area
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